BAGHDAD, June 28 (Reuters) - Iraqi security forces arrested politicians, lawmakers and senior government officials early on Sunday in what security and legal sources described as the start of a broader anti-corruption campaign ordered by Prime Minister Ali al-Zaidi.

Elite Counter Terrorism Service (CTS) units raided the homes of politicians and senior officials inside Baghdad's heavily fortified Green Zone in the early hours of Sunday and made several arrests, the sources said, declining to be named because they are not authorised to speak to media on sensitive issues.

No official statement has been made about the arrests.

Zaidi, who took office in May, has pledged to tackle entrenched corruption, one of Iraq's most persistent governance challenges despite repeated promises by successive governments to hold officials accountable.

Sunday's operation was launched on direct orders from Zaidi after Iraqi judicial authorities issued arrest warrants as part of a crackdown on what the sources described as suspected corruption networks.

The latest raids followed the recent arrest of several senior officials, including a deputy oil minister, on corruption-related charges. Those arrests led to the issuance of additional arrest warrants that were executed on Sunday, the three sources said.

Most senior Iraqi government officials, lawmakers and political leaders maintain residences or offices inside Baghdad’s Green Zone, where parliament, foreign embassies and the prime minister’s office are situated.

A senior source quoted by state news agency INA said that some of the latest arrests were based on testimony provided by Adnan al-Jumaili, deputy oil minister for refining affairs, after his detention on corruption charges. The source told INA that al-Jumaili's statements implicated a wider network of officials in alleged corruption schemes.

Some suspects managed to flee before security forces reached them, prompting authorities to close entrances to the Green Zone and launch a wider search operation, the three security and legal sources said, adding that the campaign is expected to continue over the coming days.

(Reported by Ahmed Rasheed and Muayad HameedEditing by David Goodman)